After exposure to therapeutic doses of ionizing radiation, the microvasculature must retain its ability to regenerate and grow during the healing of damaged tissues. The proposed experiments are designed to measure the radiation response of capillary growth, using a corneal neovascularization model. One set of experiments will evaluate endothelial cellular proliferation and capillary formation in response to an acute inflammatory stimulus applied to the cornea after irradiation of the resting limbal blood vessels with graded single or split doses. A second set of experiments will evaluate continued endothelial proliferation and capillary formation after irradiation of vessels already actively growing into the inflamed cornea. Radiation survival curves, based on actual formation of blood vessels and on proliferation of endothelial cells, will be constructed. Formation of blood vessels will be measured from photographs taken of temporary whole-mount preparations of corneas having colloidal carbon-perfused vessels. From the same tissue samples, Epon section autoradiography will then be performed, and proliferation (based on DNA synthesis) of endothelial cells will be assessed by quantification of the 3H-thymidine labeling index. In the evaluation of actual formation of capillaries, the process of endothelial cellular migration as well as endothelial proliferation will be studied and distinctions between the two processes will be made.